The present invention relates to a circuit configuration of ABS (Auto Band Select) mainly used for a wireless transmitter/receiver or the like and, more particularly, to the configuration of a PLL (Phase Lock Loop).
The ABS function is an indispensable technical element for a configuration of a wireless transmitter/receiver of recent years. Cellular phones each using the wireless transmitter/receiver are generally adapted to a tri-band or dual-band of, for example, 800 MHz, 900 MHz, and 2 GHz.
Shortening of process time of the ABS function is synonymous with increase in speed of phase locking of a PLL. Therefore, it is important to increase the speed of phase locking of a PLL.
In the invention described in Japanese Unexamined Patent Publication No. 2005-109618 (patent document 1), a method of determining a final selection band is disclosed, by employing a binary search method for a PLL of an open loop method and performing phase determination by the number of times according to the number of band switch control signals input to a VCO.
Since precision of ABS and process time have a tradeoff relation, to shorten the process time of the ABS, high-precision ABS is required. To realize high-precision ABS, in recent years, a method using a DPFD (Digital Phase Comparator) is becoming common.
Further, it is also considered to increase precision of a PLL by using an ADPLL (All Digital Phase Lock Loop) in which all of circuit configurations are digitized and to configure a wireless transmitter/receiver by a general semiconductor manufacturing process.
Patent Document 1: Japanese Unexamined Patent Publication No. 2005-109618